using System;
using System.Collections.Generic;
using UnityEngine.ResourceManagement;
using UnityEngine.ResourceManagement.AsyncOperations;
using UnityEngine.ResourceManagement.ResourceLocations;
using UnityEngine.ResourceManagement.Util;
using UnityEngine.SceneManagement;

namespace UnityEngine.ResourceManagement.ResourceProviders
{
	/// <summary>
	/// Wrapper for scenes. This is used to allow access to the AsyncOperation and delayed activation.
	/// </summary>
	public struct SceneInstance
	{
		Scene m_Scene;
		internal AsyncOperation m_Operation;

		/// <summary>
		/// The scene instance.
		/// </summary>
		public Scene Scene
		{
			get { return m_Scene; }
			internal set { m_Scene = value; }
		}

		/// <summary>
		/// Activate the scene via the AsyncOperation.
		/// </summary>
		[Obsolete("Activate() has been deprecated.  Please use ActivateAsync().")]
		public void Activate()
		{
			m_Operation.allowSceneActivation = true;
		}

		/// <summary>
		/// Activate the scene via the AsyncOperation.  This is the scene loading AsyncOperation provided by the engine.
		/// The documentation for AsyncOperation can be found here: https://docs.unity3d.com/ScriptReference/AsyncOperation.html
		/// </summary>
		/// <returns>The scene load operation.</returns>
		public AsyncOperation ActivateAsync()
		{
			m_Operation.allowSceneActivation = true;
			return m_Operation;
		}

		///<inheritdoc cref="Scene"/>
		public override int GetHashCode()
		{
			return Scene.GetHashCode();
		}

		/// <inheritdoc cref="Scene"/>
		public override bool Equals(object obj)
		{
			if (!(obj is SceneInstance))
				return false;
			return Scene.Equals(((SceneInstance)obj).Scene);
		}
	}

	/// <summary>
	/// Interface for scene providers.
	/// </summary>
	public interface ISceneProvider
	{
		/// <summary>
		/// Load a scene at a specified resource location.
		/// </summary>
		/// <param name="resourceManager">The resource manager to use for loading dependencies.</param>
		/// <param name="location">The location of the scene.</param>
		/// <param name="loadMode">Load mode for the scene.</param>
		/// <param name="activateOnLoad">If true, the scene is activated as soon as it finished loading. Otherwise it needs to be activated via the returned SceneInstance object.</param>
		/// <param name="priority">The loading priority for the load.</param>
		/// <returns>An operation handle for the loading of the scene.  The scene is wrapped in a SceneInstance object to support delayed activation.</returns>
		AsyncOperationHandle<SceneInstance> ProvideScene(ResourceManager resourceManager, IResourceLocation location, LoadSceneMode loadMode, bool activateOnLoad, int priority);

		/// <summary>
		/// Load a scene at a specified resource location.
		/// </summary>
		/// <param name="resourceManager">The resource manager to use for loading dependencies.</param>
		/// <param name="location">The location of the scene.</param>
		/// <param name="loadSceneParameters">Load parameters for the scene.</param>
		/// <param name="activateOnLoad">If true, the scene is activated as soon as it finished loading. Otherwise it needs to be activated via the returned SceneInstance object.</param>
		/// <param name="priority">The loading priority for the load.</param>
		/// <returns>An operation handle for the loading of the scene.  The scene is wrapped in a SceneInstance object to support delayed activation.</returns>
		AsyncOperationHandle<SceneInstance> ProvideScene(ResourceManager resourceManager, IResourceLocation location, LoadSceneParameters loadSceneParameters, bool activateOnLoad, int priority);

		/// <summary>
		/// Release a scene.
		/// </summary>
		/// <param name="resourceManager">The resource manager to use for loading dependencies.</param>
		/// <param name="sceneLoadHandle">The operation handle used to load the scene.</param>
		/// <returns>An operation handle for the unload.</returns>
		AsyncOperationHandle<SceneInstance> ReleaseScene(ResourceManager resourceManager, AsyncOperationHandle<SceneInstance> sceneLoadHandle);
	}

	internal interface ISceneProvider2 : ISceneProvider
	{
		/// <summary>
		/// Release a scene.
		/// </summary>
		/// <param name="resourceManager">The resource manager to use for loading dependencies.</param>
		/// <param name="sceneLoadHandle">The operation handle used to load the scene.</param>
		/// <returns>An operation handle for the unload.</returns>
		AsyncOperationHandle<SceneInstance> ReleaseScene(ResourceManager resourceManager, AsyncOperationHandle<SceneInstance> sceneLoadHandle, UnloadSceneOptions unloadOptions);
	}

	static internal class SceneProviderExtensions
	{
		public static AsyncOperationHandle<SceneInstance> ReleaseScene(this ISceneProvider provider, ResourceManager resourceManager, AsyncOperationHandle<SceneInstance> sceneLoadHandle,
			UnloadSceneOptions unloadOptions)
		{
			if (provider is ISceneProvider2)
				return ((ISceneProvider2)provider).ReleaseScene(resourceManager, sceneLoadHandle, unloadOptions);
			return provider.ReleaseScene(resourceManager, sceneLoadHandle);
		}
	}
}
